Method and apparatus for generating controlled torques on objects particularly objects inside a living body

ABSTRACT

A method and apparatus for generating a controlled torque of a desired direction and magnitude in an object within a body, particularly in order to steer the object through the body, such as a catheter through a blood vessel in a living body, by producing an external magnetic field of known magnitude and direction within the body, applying to the object a coil assembly including preferably three coils of known orientation with respect to each other, preferably orthogonal to each other, and controlling the electrical current through the coils to cause the coil assembly to generate a resultant magnetic dipole interacting with the external magnetic field to produce a torque of the desired direction and magnitude.

This application claims the benefit of provisional application No.60/085,652 filed May 15, 1998.

FIELD AND BACKGROUND OF THE INVENTION

The present invention relates to a method and apparatus for generatingcontrolled torques on objects. The invention is particularly useful forgenerating controlled torques in order to steer objects through a livingbody for purposes of performing minimally-invasive diagnostic orinterventional procedures, and the invention is therefore describedbelow with respect to such an application.

BACKGROUND

Minimally-invasive diagnostic or interventional procedures require threeclasses of devices—viewing devices to provide feed-back to the operator(since direct viewing as in open surgery is not available), operationaldevices (i.e. tools to perform the task), and controller devices whichmanipulate or navigate the operational devices. Most commonly, viewingdevices are based on optical instrumentation with optic fibers orimaging modalities like X-ray, ultrasound, computerized tomography (CT)or magnetic resonance imaging (MRI). The operational devices vary withthe procedure—endoscopes and catheters for diagnostic and interventionalprocedures; and miniature specialized tools for laparoscopic and otherminimally-invasive interventions. The control of the devices is mostcommonly achieved by mechanical mechanisms. Examples include: 1)endoscopes, which are inserted into a lumen (e.g. the gastro-intestinaltract, the bronchial tree), are navigated by viewing through theendoscopes, and have mechanical control of the tip direction; 2)catheters which are inserted through blood vessels, either veins orarteries, to perform diagnostic procedures (e.g. coronarycatheterization) or interventions (e.g. angioplasty of stenosed bloodvessels or cardiac valves), and are navigated by mechanical manoeuvres(e.g. combinations of pushing, pulling and twisting of the externalportion of the catheter) together with real-time viewing of the bloodvessels and the catheters using X-ray imaging; and 3) various rigiddevices for cellular aspiration, tissue biopsy, or other diagnostic andinterventional procedures, which are inserted with real-time guiding(e.g. by ultrasound) or by stereotaxis guidance.

Computer-assisted stereotaxis is a valuable technique for performingdiagnostic and interventional procedures, most typically with the brain.During traditional stereotaxis, the patient wears a special halo-likeheadframe, and CT or MRI scans are performed to create athree-dimensional computer image that provides the exact location of thetarget (e.g. tumor) in relation to the headframe. When this technique isused for biopsy or minimally-invasive surgery of the brain, it guidesthe surgeon in determining where to make a small hole in the skull toreach the target. Newer technology is the frameless technique, using anavigational wand without the headframe (e.g. Nitin Patel and DavidSandeman, “A Simple Trajectory Guidance Device that Assists Freehand andInteractive Image Guided Biopsy of Small Deep Intracranial Targets”,Comp Aid Surg 2:186-192, 1997).

Many of the advantages of MRI that make it a powerful clinical imagingtool are also valuable during interventional procedures. The lack ofionizing radiation, and the oblique and multiplanar imagingcapabilities, are particularly useful during invasive procedures. Theabsence of beam-hardening artifacts from bone allows complex approachesto anatomic regions that may be difficult or impossible with otherimaging techniques such as conventional CT. Perhaps the greatestadvantage of MRI is the superior soft-tissue contrast resolution, whichallows early and sensitive detection of tissue changes duringinterventional procedures. Many experts now consider MRI to be one ofthe most powerful imaging techniques to guide interventionalinterstitial procedures, and in some cases even endovascular orendoluminal procedures (Yoshimi Anzai, Rex Hamilton, Shantanu Sinha,Antonio DeSalles, Keith Black, Robert Lufkin, “Interventional MRI forHead and Neck Cancer and Other Applications”, Advances in Oncology, May1995, Vol 11 No. 2).

Virtually all current guiding and manipulation methods are based onvarious mechanical or electro-mechanical modules. For example, steerablecatheters use tension wires to bend the tip of the catheter to thedesired direction, and typically enable bending in one plane; endoscopeshave mechanical control of the tip direction in two orthogonal planes,using two knobs on their control unit; rigid devices are orientedexternally before they are inserted into the body to reach the definedtarget. The major drawback of these mechanisms is their relativecomplexity and high cost, which typically result with devices formultiple use.

A somewhat different approach to navigation and manipulation is based onmagnetic stereotaxis. Current stereotactic procedures with rigiddevices, although less invasive than open surgery, may still damagevarious structures along the path of insertion. The magnetic stereotaxisinstrumentation (Stereotaxis Inc., St. Luis, Mo.) is less destructive.According to this technique surgeons insert a magnetic pellet the sizeof a rice grain into a small hole drilled into the skull of a patient,and the patient's head is then placed in a housing which contains sixsuperconducting magnets. Using previously recorded MRI or CT images orreal-time X-ray imaging as a guide, the surgeon directs the pelletthrough the brain by adjusting the forces of the various magnets. Thepellet could tow a catheter, electrode or other device to the target.However, magnetic stereotaxis cannot be used with real-time MRI becauseof the MRI scanner's strong magnetic field, which precludes the use ofmagnetic objects inside the body during MRI scanning.

From the presented background on current methodologies, one can definethe ideal system for minimal invasive procedures: It should providereal-time, 3-dimensional, non-ionizing imaging (like MRI or ultrasound)as feed-back to the user for optimal insertion and intervention; and itshould implement flexible, miniaturized devices which can be manoeuvredthrough an optimal path to minimize damage to healthy tissues andsensitive organs.

OBJECTS AND BRIEF SUMMARY OF THE INVENTION

One object of the present invention is to provide a method and apparatusfor generating controlled torques to be applied to objects, which methodand apparatus are particularly useful for maneuvering miniaturizeddevices through an optimal path in a living body to minimize damage tohealthy tissues and sensitive organs.

Another object of the present invention is to provide a method andapparatus to control and manipulate a device inside a living bodythrough the generation of magnetic dipoles in the device which interactwith an external magnetic field, like the magnetic field of an MRIsystem, and thus generate torque or torques for controlling andmanipulating the device.

DESCRIPTION OF PREFERRED EMBODIMENTS

According to one aspect of the present invention, there is provided amethod of generating a controlled torque of a desired direction andmagnitude in an object within a living body, comprising: producing anexternal magnetic field of known magnitude and direction within thebody; applying to the object a coil assembly including at least threecoils whose axes are of known orientation with respect to each other andhave components in the three orthogonal planes; and controlling theelectrical current through the coils to cause the coil assembly togenerate a resultant magnetic dipole interacting with the externalmagnetic field to produce a torque of the desired direction andmagnitude.

According to further features in the preferred embodiment describedbelow, the coils have axes oriented orthogonally with respect to eachother; and the external magnetic field is a steady, homogenous magneticfield, particularly the main magnetic field of an MRI (MagneticResonance Imaging) system.

MRI is rapidly becoming the preferred methodology for minimal invasivediagnostic and interventional procedures because of itsnon-invasiveness, high resolution, high contrast between different softtissues, and absence of shadowing by bones. Recent technologicalimprovements in MRI systems provide rapid scanning sequences, whichenable real-time imaging during the procedure, and an open architecturewhich enables access to the patient. The present invention makes use ofa basic, universal component of the MRI system—the steady, homogenousmagnetic field B0, typically generated by a superconductingelectromagnetic coil; but the invention may also be applied with othersources of external or internal magnetic fields.

Any magnetic field exerts torque on magnetic dipoles, like the onegenerated by an electrical current in a closed-loop wire or a coil(Biot-Savart and Ampere Laws). The torque on the coil depends on therelative direction of the dipole with respect to the direction of themagnetic field. With at least three coils, for example three orthogonalcoils, a magnetic dipole with any spatial direction can be generated:each coil generates a dipole, which can be represented by a vector, andthe combined three coils generate a dipole which is the vectorial sum ofthe three dipoles.

One can generate such a dipole with any magnitude and direction bycontrolling the electrical currents through each of (he three individualcoils, which determine the magnitude of the dipole in each coil. If theorientation of the three coils in the magnetic field is known, aspecific magnetic dipole (i.e. with specific magnitude and direction)can be generated. This controllable dipole interacts with the externalmagnetic field to generate a controllable torque, namely a torque with aspecific magnitude and direction.

The generated torque can be used to bend the tip of a catheter orendoscope and thus to enable the operator to advance the device in therequired direction. Furthermore, the torque can be used to operatevarious devices to perform different activities inside the body, similarto mechanical devices used during laparoscopic procedures. For example,a pliers-like clamping mechanism can be used to hold or release objectsinside the body; a miniature cutting device can be used to performremote surgery; and a miniature stapler-like device can be used tosuture structures.

The present invention has significant advantages over existingmethodologies. Compared with mechanical devices for navigation andoperation of various diagnostic and interventional devices,electromagnetic devices constructed in accordance with the presentinvention for the same tasks will be smaller, cheaper, and will enablemore precise control of the position, direction and operation of thedevice.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is herein described, by way of example only, withreference to the accompanying drawings, wherein:

FIG. 1 is a block diagram illustrating one form of apparatus constructedin accordance with the present invention for use in an MRI system forsteering an intra-body operational device in order to perform adiagnostic or interventional procedure;

FIG. 1a more particularly illustrates one form of torque-generatingmodule in the apparatus of FIG. 1;

FIGS. 2a and 2 b schematically illustrate the use of a joy stick forcontrolling the position and direction of an intra-body device, such asthe tip pf a catheter, endoscope, or optical fiber,

FIGS. 3a and 3 b schematically illustrate the use of a joy stick with aslide for controlling the operation of an intra-body miniature tool,such as a clamping, cutting, or stapling device;

FIG. 4 is a diagram more particularly illustrating the operation of thelocation and direction module (LDM) in the apparatus of FIG. 1;

FIG. 5 is a diagram which explains our way to generate a magnetic dipolein the torque generating module in order to rotate or bend theintra-body device or part of it to a new direction;

FIGS. 6a and 6 b diagrammatically illustrate, in a simplifiedtwo-dimensional display, the manner of creating a specific magneticdipole by summing the dipoles generated by three orthogonal coils; and

FIG. 7 illustrates the functioning of the invention in steering a deviceduring MRI imaging.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The following description relates to a preferred embodiment of theinvention, namely to a system for generating controllable torques in adevice under MRI imaging. For the sake of simplicity, the preferredembodiment is presented with reference to the use of an MRI system'smagnet field, but the invention may be implemented with other sources ofexternal or internal magnetic fields. Potential clinical applications ofthe described core technology are described. In the following, vectorsare underlined, to distinguish them from scalars.

The apparatus illustrated in FIG. 1 includes a processing and controlunit 10, a torque-generating module (TGM) 20, which is incorporated inan intra-body device 30, and an electronic interface unit 12. Theintra-body device 30 is manipulated through the interaction between thehomogenous, main magnetic field (B0) of the MRI system 40, which isgenerated by the MRI magnet 42, and the magnetic dipoles generated bythe micro-coils 22, 24, 26 in the torque-generating module 20.

The coils 22, 24, 26, as more particularly illustrated in FIG. 1a, haveaxes of known orientation with respect to each other, which axes havecomponents in the three orthogonal planes. Preferably, their axes areoriented orthogonally with respect to each other as shown in FIG. 1a. Aswill be described more particularly below, the electrical currentsthrough coils 22, 24, 26 may be controlled by the processing and controlunit 10 to cause the torque generating module 20 to generate a resultantmagnetic dipole interacting with the homogenous magnetic field producedby the MRI magnet 42 to produce a torque of the desired direction andmagnitude, which is applied to the intra-body device 30, to steer it orto otherwise activate it.

The processing and control unit 10 interacts with the MRI computer 44and with the gradient activation control unit 48 which provide theprocessing and control unit with information on the MRI systemelectro-magnetic gradient fields (B1), generated by the set of threeorthogonal gradient coils 43, and the timing sequence of the activationof the these coils during MRI scanning. The MRI system provides theoperator with a real-time image of the operation field through eitherthe standard MRI display or a specialized monitor 46. An optionallocation and direction module (LDM) 50 may be incorporated into theintra-body device 30 to provide its location and direction ororientation.

In FIG. 1, the MRI system 40 provides the operator with a real-timedisplay 46 of the body. The MRI computer 44 provides the processing andcontrol unit 10 with the spatial distribution of the gradient magneticfields as a function of time, to enable real-time localization of thedevice. The computer 44 also provides the processing and control unit 10with the event schedule of the MRI system to prevent image artifacts dueto the activation of the torque-generating module (TGM) 20 when the MRIgradient fields are activated for imaging. The MRI computer 44 can beprogrammed to perform real-time imaging of the region around the currentlocation of the intra-body device 30 to enable fast update of the imageas the device is advanced or is manipulated by the operator.

Typically, the operator manipulates the device 30 by controlling atorque on specific parts of the device, which are termed the manipulatedparts. For example, FIGS. 2a and 2 b illustrate how the intra-bodydevice 30, such as a catheter, endoscope, or optical fiber, can bedirected through a passageway 32, such as blood vessel bifurcations, thebronchial tree, or the gastrointestinal tract, by bending its leadingtip to the required direction by manipulating a joystick 16 of an inputdevice 14 to the processing and control unit 10.

FIGS. 3a and 3 b illustrate how a miniature clamp 130 can be opened orclosed by exerting torques on its jaws by manipulating a slide 118 onthe input device 114, which input device also includes a joystick 116 tosteer the miniature clamp 130 to the proper location.

The location and direction of the intra-body device 30 (or 130) and itsmanipulatable parts are either measured from the MRI images, or aredetermined by an optional location and direction module (LDM) 50 (FIG.1). The capability of location tracking by the MRI is available with anycommercial system, provided that the intra-body device is made ofmaterial having high contrast with biological tissues (e.g. Smits HFMand Bakker CJG, “Susceptibility-Bases Catheter Visualization”, in“Interventional Magnetic Resonance Imaging”, edited by Debatin J F andAdams G, Springer, 1998) or has a small receiving coil which issensitive to near-neighbourhood emitted radio-frequency signal duringthe MR imaging process (Dumoulin C L, Darro R D, Souza S P, “MagneticResonance Tracking”, in “Interventional MR”, edited by Jolesz F A andYoung I Y, Mosby, 1998).

FIG. 4 illustrates an approach to sense the location of the device usinga dedicated module, namely, the location and direction module (LDM) 50,which comprises of a set of three sensing coils. The three sensing coilsmay be the sane three coils 22, 24, 26 of the torque-generating module(TGM) 20, or another set of coils optimized for their use in the LDM.

The MRI alternating gradient magnetic fields (B1) induce electromotiveforces (E) in the sensing coils, and the magnitudes of the inducedelectromotive forces are related to the magnetic flux Θ through thecoil, as given by Faraday Law:

E=−dΘ/dt  (1)

where the magnetic flux Θ is determined by the total magnetic field(B=B0 +B1 ), the coils effective area (which in a case of coil withmultiple loops equals the sum of the area of all the loops in the coil),and the direction of the magnetic field with respect to the spatialorientation of the coil, which is defined by the direction of a unitvector n vertical to the coil surface:

Θ=B·nA  (2)

where the dot denotes a vectorial dot product and A is the coil area.

FIG. 4 shows how the magnitudes of the induced electromotive forces andthe known magnetic field B at each point in the operating field (assupplied by the MRI system's computer) enable the calculation of thebody location and direction by Equations 3 and 4, set forth below. Thissimplified 2-dimensional presentation of FIG. 4 includes only twomeasured values E1 and E2, while the full realization of the systemrequires three values E1, E2, E3 and the corresponding three-dimensionalequations. Thus for two dimensions the direction and location will bedetermined by:

θ=arctan(E ₂ /E ₁)  (3)

(dB/dt)² =E ₁ ² +E ₂ ²  (4)

where θ is the direction of the tip of the intra-body device 30 withrespect to the magnetic field direction, and E₁ and E₂ are the inducedelectromotive forces in the two orthogonal coils, and B is the magnitudeof the magnetic field vector B. The electromotive forces are measured byelectrical circuitry in the electronic interface unit 12, and themeasured values are supplied to the processing and control unit 10,which calculates the direction θ and the time-derivative of the magneticfield magnitude B. Since the homogenous field B0 does not change withtime, the electromotive forces are determined by the variable magneticfield B1 of the gradient coils, and equation 4 can be rewritten as:

(dB 1/dt)² =E ₁ ² +E ₂ ²  (5)

The main advantage of the disclosed methodology—it enables sensing ofthe device location and direction without the need for MRI imaging, soservo control of the required manipulation of the device is feasible.Real-time control of the device may be of particular interest with someof the clinical applications as presented below.

The processing and control unit 10 receives the time-variable magnitudeof the magnetic gradient fields B1 from the MRI system 40 during theactivation of the gradient coils. The instantaneous location of thesensing coils is determined by the processing and control unit 10 bycomparing the calculated value dB1/dt to the supplied values of thefield B1, and finding the spatial location at which the calculated valueof dB1/dt is equal to the generated one.

Knowing the location and direction of the intra-body device and themanipulated parts, the MRI display 46 presents this information inaddition to the MR image. For example, during navigation of a catheteror endoscope, the MR image can be displayed in the device's coordinatesystem, as if the operator is looking forward from the device, with asynthetic representation of the tip direction. Alternatively, the imageand the intra-body device can be displayed by using standard MRI viewsand sections. Using real-time LDM sensing enables real-time display ofthe device location and direction to the operator. However, othertracking methodologies can be used instead of the LDM module.

Based on the composite MRI display of the imaged body and the intra-bodydevice, the operator manipulates the device using a standard inputdevice 14. As described above, the direction of a catheter tip can becontrolled by using a joystick 16 (FIG. 2a). The operator identifies therequired direction to move the catheter by interpretation of the MRimage and simply moves the joystick 16 towards the required newdirection (FIG. 2b). FIGS. 3a and 3 b, also described above, illustrateanother example involving the operation of a clamp 130, where theoperator can use the joystick 116 of input device 114 to control thedirection of the clamp 130 and a slide 118 to control opening andclosing of the clamp.

The commands from the input device are fed into the processing andcontrol unit 10, which calculates the required rotation of themanipulated part in the device (e.g. the tip of a catheter or opticalfiber) as determined by the input command and the current direction ofthis part in reference to the device (e.g. the current direction of thetip). Knowing the direction of the main magnetic field B0 of the MRIsystem, the processing and control unit calculates the direction of themagnetic dipole which is required to produce the torque of the requiredmagnitude and direction to manipulate the part, for example to rotatethe tip of a catheter to the new direction. The magnetic field generatesa torque which rotates the magnetic dipole until it reaches anequilibrium state where the direction of the dipole aligns with thedirection of the magnetic field.

More specifically, once the direction of the device in the MRIcoordinate system is known, a plane containing the device line ofdirection and the magnetic field B0 line of direction is determined.Referring now to FIG. 5, which presents this plane, the angle betweenthe magnetic field direction and the current direction of the device 30is denoted β. For the sake of simplicity in the presentation, thedesired direction of the device, as determined by the input from theinput device 14. is presented in the same plane (i.e. this is asimplified 2-dimensional case) and forms an angle δ with the currentdirection of the device. In order to bend the tip of the device to thenew direction defined by the angle δ, a dipole is generated in adirection α, with respect to the current direction of the device, wherethe angle α given by:

α=β−δ  (6)

If the angle α is maintained throughout the steering maneuver, themagnetic dipole μ interacts with the magnetic field B0 to generate atorque which bends the device until it aligns with the desireddirection, at that time the dipole aligns with the direction of themagnetic field B0 and the resultant torque diminishes to zero. Otherimplementations can be used, like using a variable dipole directionwhich maximizes the generated torque to induce faster bending orrotation of the tip. If a real-time feedback is available by using theLDM 50, then optimal control of the manipulation can be achieved byusing servo control of the dipole generation (e.g. by PID controller).

Referring now to FIG. 6a, the magnetic dipole in the torque-generatingmodule (TGM) 20 is generated in the required direction by controllingelectrical currents in the three micro-coils 22, 24, 26 of the TGM. Thepreferred embodiment is with three orthogonal coils, however otherconfigurations with one, two, or more than three coils can be used forspecific applications.

The net dipole in the TGM is calculated by vectorial sum of the threeindividual magnetic dipoles which are generated by the three coils 22,24, 26:

μ=μ ₁+μ ₂+μ ₃  (7)

The high intensity homogenous magnetic field B0 of the MRI systeminteracts with the magnetic dipole and generates a torque on theactivated part of the device, e.g. the tip of the catheter, endoscope,or optical fiber:

τ=μ {circumflex over (x)}Bo   (8)

where τ is the generated torque, μ is the magnetic dipole, {circumflexover (x)} is the vectorial cross product and Bo is the vectorialrepresentation of the magnetic field B0 of the MRI system.

The manipulated part bends or rotates into the required direction andthus enables the operator to conduct the required task, for example tonavigate the device through an optimal path to minimize damage to tissueor into a bifurcation in blood vessel or another lumen. In most MRIsystems the steady, homogenous uni-directional magnetic field B0 limitsthe possible directions of the generated torque to off-axial directions.For example, for MRI system with magnetic field in the Z-direction (thebody axial direction), a device positioned in the two transversedirections can be bent in one plane and rotated around its axialdirection, while a device positioned in the Z-direction can be bent inany direction but cannot be rotated. Although this may impose somelimitations on the operation of the device, correct planning of theprocedure, for example choosing the insertion point of the device, canovercome this limitation. Furthermore, any direction can be achieved bycombining two manipulations in the effective directions. For example, tobend the tip in the Y direction, the tip can be initially bent in the Xdirection and then the device can be rotated by 90 degrees. Otherpotential solutions include the combination of mechanical manipulationmechanisms with the present invention to achieve an unlimited spatialmanoeuverability or the use of an electromagnet to add a magnetic fieldin transverse direction to the main MRI magnetic field.

During the manipulation of the device, the MRI system may continuescanning the body. To prevent distortion of the image due to themagnetic field of the generated dipole, the processing and control unitsuspends the operation of the torque-generating module when the MRIsystem activates the gradient fields and is sensitive to smalldistortions of the magnetic field geometry. With fast MRI scanners thesepauses are relatively short and may not be sensed by the operator. Thecontinuous real-time imaging enables the continuous update of the imagewith the device in it for optimal performance by the system's operator.

FIG. 7 is a flow chart illustrating the operation of the processing andcontrol unit 10, FIG. 1. First the patient undergoes a baseline MRIscanning of the region of interest (ROI) to be used as a reference image704. The operator inserts the device into the body and advances it intothe ROI. The location and direction variables 720 in the MRI coordinatesystem are determined by the processing and control unit 10 byprocessing input signals 700 from the LDM during activation of thegradient fields of the MRI system. The location and direction variables720 are used to generate a composite image 730 of the device on thereference image 704.

The operator then determines the new direction of the device andprovides the desired direction 706 as a command from the input device tothe processing and control unit 10. The processing and control unitcalculates the difference 740 between the current direction of thedevice and the desired direction of the device. The processing andcontrol unit determines the required direction of the magnetic dipole750 by using Equation 6.

The magnitude of the required dipole is determined by technical andsafety constraints, for example the maximal permitted heating of thecoils. The processing and control unit calculates the required dipoles760 in the three coils of the TGM, using the determined magnitude anddirection of the required magnetic dipole and the current direction ofthe device. The processing and control unit activates drivers togenerate electrical currents in the three coils in order to result withthe required dipoles in the three coils 770. The generated dipoleinteracts with the magnetic field B0 of the MRI and bends the tip of thedevice 780. At the same time the operator can move the device, forexample to push it into a new location.

The process is now repeated, the new location and orientation 720 aredetermined and the updated location of the device on the reference imageis presented to the operator to continue the steering of the device.

If high precision is required, or to enable the use of the inventionwith a dynamic ROI (e.g. moving ROI due to breathing or cardiaccontraction), the device manipulation can be sequenced with rapid MRIscans which are used to refresh the baseline MRI image 704 and toprovide a dynamic reference image.

Potential clinical applications of the invention include the navigationof various instruments through various organs, cavities or lumens in thebody to perform either diagnostic or therapeutic interventions. Theinvention can be used to navigate instruments through the pulmonarysystem (the bronchial tree or blood vessels), the cardiovascular system(heart chambers, blood vessels), the gastro-intestinal tract (stomach,duodenum, biliary tract, gall bladder, intestine, colon), the liver, theurinary system (bladder, ureters, kidneys), the skeletal system(joints), the genital organs, the brain (internally through theventricles or blood vessels or externally through a burr hole in thescull). The invention enables navigation through these organs to reach aspecific location and to perform diagnostic procedures (e.g. biopsy,aspiration, direct viewing) and therapeutic procedures (e.g. local drugdelivery, ablation, cryo-therapy, gene delivery, etc.).

For example, the invention may be implemented in the following devices:

1. Steerable catheters—the torque-generating modules (TGM) can replacethe complex and costly tension wires used to manipulate the tip ofsteerable catheter and enable mass production of low-cost, single usesteerable catheters.

2. Flexible endoscope—as with the steerable catheters, the TGM canreplace the currently used mechanical system of controlling theendoscope tip and enable cheaper and thinner endoscope. Furthermore, theuse of an input device like a joystick rather than two separate knobswill enable easier operation of the endoscope.

3. Rigid endoscope—a flexible, sliding tip with TGM can be integratedinto the rigid endoscope to enable final, precise navigation inside thetarget, after it was inserted with the rigid endoscope, or to enable theapplication of specific intervention in multiple directions without theneed to move the rigid device.

4. Optic fibers for laser therapy—the TGM can be used to control thedirection of the fiber's tip and enable more accurate laser therapyunder MRI control.

While the invention has been described with respect to several preferredembodiments, it will therefore be appreciated that these are set forthmerely for purposes of example, and that many other variations,modifications and applications of the invention may be made.

What is claimed is:
 1. A method of generating a controlled torque of adesired direction and magnitude in an object within a body, comprising:producing an external magnetic field of known magnitude and directionwithin said body, said magnetic field having a coordinate system;applying to said object a coil assembly including at least three coilswhose axes are of known orientation with respect to each other, and havecomponents in three orthogonal planes; tracking the orientation of saidobject with respect to the coordinate system of said external magneticfield; applying an electrical current and controlling the electricalcurrent through said coils to cause the coil assembly to generate aresultant magnetic dipole interacting with said external magnetic fieldto produce a torque of said desired direction and magnitude.
 2. Themethod according to claim 1, wherein said body and said object areimaged on a display during the steering of the object within said body.3. The method according to claim 1, wherein said step of producing anexternal magnetic field comprises producing an external magnetic fieldby an MRI (Magnetic Resonance Imaging) system, and wherein said step oftracking comprises using the gradient fields of said MRI system as areference field for tracking.
 4. A method of steering a medical devicethrough a passageway within a body, comprising: producing an externalmagnetic field of known magnitude and direction within said body, saidmagnetic field having a coordinate system; providing a medical devicelocated within said body; applying to said medical device at least onecoil; tracking the orientation of said medical device with respect tothe coordinate system of said external magnetic field; applying anelectrical current and controlling the electrical current through saidcoil to cause it to generate a resultant magnetic dipole interactingwith said external magnetic field to produce a torque steering saidmedical device in a desired direction.
 5. The method according to claim4, wherein said step of producing an external magnetic field comprisesproducing an external magnetic field by an MRI (Magnetic ResonanceImaging) system.
 6. The method according to claim 5, wherein said stepof tracking comprises using the gradient fields of said MRI system as areference field for tracking.
 7. Apparatus for generating a controlledtorque of a desired direction and magnitude to be applied to an objectwithin a body, comprising: means for producing an external magneticfield of known magnitude and direction within said body, said magneticfield having a coordinate system; an object adapted to be located withinsaid body; a coil assembly attached to said object and including atleast three coils whose axes are of known orientation with respect toeach other, and have components in three orthogonal planes; means fortracking the orientation of said object with respect to the coordinatesystem of said external magnetic field; and a drive system for applyingcontrolled electrical current trough said coils to cause the coilassembly to generate a resultant magnetic dipole interacting with saidexternal magnetic field to produce a torque of said desired directionand magnitude.
 8. The apparatus according to claim 7, wherein said coilshave axes oriented orthogonally with respect to each other.
 9. Theapparatus according to claim 7, wherein said external magnetic field isa steady, homogenous magnetic field.
 10. The apparatus according toclaim 7, wherein said object is a medical device to be steered by saidcontrolled torque through a path within a living body to perform adiagnostic or interventional procedure.
 11. The apparatus of accordingto claim 10, wherein said medical device is selected from the groupconsisting of a catheter, endoscope, or optical fiber.
 12. The apparatusaccording to claim 10, wherein said medical device is a biopsy orsurgical tool.
 13. The apparatus according to claim 7, wherein saidapparatus further includes an MRI system having a display for imagingsaid body and said object during the steering of the object through saidbody.
 14. The apparatus according to claim 7, wherein said means forproducing an external magnetic field comprises an MRI (MagneticResonance Imaging) system, and wherein said means for tracking comprisesthe gradient fields of said MRI system as a reference field fortracking.
 15. Apparatus for steering a medical device through apassageway within a body, comprising: a medical device adapted to belocated within said body; means for producing an external magnetic fieldof known magnitude and direction within said body; at least one coilattached to said medical device; means for tracking the orientation ofsaid medical device with respect to the coordinate system of saidexternal magnetic field; and a drive system for applying controlledelectrical current through said coil to cause the coil to generate aresultant magnetic dipole interacting with said external magnetic fieldto produce a torque steering said medical device in a desired direction.16. The apparatus according to claim 15, wherein said coil is a part ofa coil assembly having at least two coils whose axes are of knownorientation with respect to each other and have components in at leasttwo different orthogonal planes.
 17. The apparatus according to claim16, wherein said coil assembly includes three coils having axes orientedorthogonally with respect to each other.
 18. The apparatus according toclaim 15, wherein said means for producing an external magnetic fieldcomprises an MRI (Magnetic Resonance Imaging) system.